Lignocellulose board



Patented Aug. 3, 1954 LIGNOCELLULOSE BOARD Albert C. Lighthall, Denver,0010., and Arthur B.

Anderson,

Portland, Oreg.; Lyllian F. Lightliall,

administratrix of said Albert C. Lighthall, de-

ceased No Drawing. Application June 15, 1949, Serial No. 99,357

7 Claims. 1

The present invention relates to composite products comprising particlesof wood or other lignocellulose material and, as a binding and waterrepellant constituent, defibrated coniferous lignocellulose rich inacetone soluble content from coniferous species of trees andcharacterized by solubility in organic solvents.

In making composition boards and similar consolidated fibrous products,wood or other lignocellulose material such as cane, corn stalks, strawand the like conventionally are reduced to fiber or particle form. Theresulting finely divided material is formed into a felt or mat, whichthen is heated with or without the application of substantial pressure.When substantial pressure is not applied during the heating operation,the product is porous and of low density and finds its principalapplication as insulation board. Where, however, substantial pressure isapplied during the heating operation, the particles of lignocellulosematerial are consolidated to form a board of relatively high densitywhich is used extensively as hardboard, panel board, flooring, and thelike.

The strength and water resistance of fibrous composition products suchas consolidated fiber boards obviously are of primary importance indetermining their suitability for use in the customary applications. Toimprove the strength of the products, it is usual practice toincorporate therein substantial amounts of binders such as phenolicresins, urea resins, decayed wood and the like. These may be added toand intimately mixed with the finely divided material prior to itsformation into a felt and consolidation. A1- ternatively, they may besprinkled or sprayed on the felt, after which the latter is pressed toform the final product. Similarly, in order to prevent the swelling andwarping oi the fibrous products upon their exposure to moistenvironments, materials conventionally are incorporated therein whichprevent the absorption of water and thus impart dimensional stability tothe products. A variety of such materials commonly are employed, theusual ones being paper makers sizing materials such as rosin, sodiumrosinate, waxes, starch, dextrin, various gums, albumin, casein, and thelike.

Where sizing materials are used, they customarily are mixed with thefiber before being formed into boards. Substantial amounts areemployed, 1. e. amounts of several per cent by weight, in orderefiectively to coat the fibers and prevent the absorption of moistureinto the same by capillary attraction. A common method of incorporatingthe size comprises adding it to the aqueous pulp suspension in the pulpchest just ahead of the head box of the wet forming machine. Tofacilitate a thorough dispersion throughout the pulp, it usually isadded in the form of sodium rosinate, if a rosin size is employed, or asan aqueous alkaline wax dispersion, if a wax size is used. After theaddition of the sizing agent, the mixture then is agitated thoroughly,after which alum or mineral acid is added in amount sufiicient to adjustthe pH of the pulp mixture to a level of pH 4 to pH 5.5. This convertsthe sodium rosinate to insoluble rosin in the one case, and destroys thewater miscible wax emulsion in the other case, so that the sizing agentis deposited on the fibrous material.

In addition to the use of sizing agents, other devices frequently areresorted to for improving the water repellancy of fiber boards. Forexample, the board may be conditioned in a drying oil followed .by aheat treatment. Alternatively, the board may be subjectedtohightemperatures without the use of a drying oil. Still further,resins and other materials may be used as water repelling agents. Itwill be obvious, however, that these various expedients for increasingthe strength and water resistance of the boards add materially to thecost of their manufacture, because of the added expense of the necessarymaterials, labor and equipment.

We now have discovered that fiber boards and other composite fibrousproducts of high strength and water resistance may be formed by theinclusion in the products of the extractive material present in thewoods of coniferous species,

of trees, and characterized by solubility in acetone and other neutralorganic solvents. Such species include the Ponderosa pine, the sugarpine, the Idaho white pine, the Jeffery pine, the long leaf pine, andother southern pines, the Douglas fir, the Noble fir, the hemlocks, thespruces, the redwoods, and the like.

As used herein, the terms acetone-soluble content and wood extractivematerials, comprehends the non-integral elements of the cell structureof wood tissue which are soluble in neutral organic solvents such asacetone. They comprise a complex mixture of organic substances,including fatty acids, phenolic compounds, volatile terpenes, esters,sterols, fats, waxes, resin acids, and the like. Such materials, ascompared with the cellulose, hemicellulose and lignin do not form anintegral part of the cell structure or the wood. They normally are founddistributed throughout the sap wood or heart wood of the coniferousspecies of trees in amounts of from 2% to 4% by weight, or less. Theyare concentrated, however, in other fractions of the wood such as theknots, which may contain from 25% to 43% by weight of woodextractives,the stump heartwood which may contain from 11% to 36% byweight of wood extractives, and the massed pitch areas which may containup to 50% of these materials. These extractive rich wood fractions areknown colloquially in certain areas of the United States as light woodor as fat wood.

As indicated above, the extractive materials may be isolated from thecell structure of the wood by extraction, with neutral organic solvents,by which is meant organic solvents which are neither acidic nor basic.Such solvents include broadly the hydrocarbon solvents, the alcohols,the esters, the ketones, and the ethers. Representative of the aliphatichydrocarbon solvents are the hexanes, the cyclohexanes, the heptanes,the octanes, and the mixed hydrocarbon fractions including petroleumether, naphtha, gasoline, kerosene, etc. Illustrative of the aromatichydrocarbon solvents which may be used in the isolation of extractivematerials from wood are benzene, toluene, the xylenes, the methyl ethylbenzenes, etc.

Typical of the alcohols which may be used for the purposes of thepresent invention are methyl alcohol, ethyl alcohol, propyl alcohol,isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, the amyl alcoholsand the like.

Illustrative esters which may be used in the isolation of extractivematerials from wood are methyl acetate, ethyl acetate, propyl acetate,butyl acetate, methyl propionate, ethyl propionate, propyl propionate,butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate,butyl butyrate, etc.

Ketones which may be used to isolate extractive material from woodinclude acetone, methyl ethyl ketone, methyl propyl ketone, methylisopropyl ketone, ethyl propyl ketone, ethyl isopropyl ketone, di-propylketone, di-isopropyl ketone, methyl n-butyl ketone, methyl isobutylketone and the like.

Typical others which may be used to isolate extractive materials fromwood are: methyl ethyl ether, di-ethyl ether, methyl n-propyl ether,methyl isopropyl ether, ethyl n-propyl ether, ethyl isopropyl ether,methyl butyl ether, ethyl butyl ether, propyl butyl ether, etc.

The foregoing and other neutral organic solvents may be used singly orin combination with each other to remove the extractive materials fromwood, by first reducing the wood to the form of small particles, andthen treating the particles with the selected solvent or solventmixture. The treatment preferably is effected in a continuous extractionapparatus, using the solvent at about its boiling temperature. After theextraction is complete, the solvent may be removed by distillation fromthe extractive materials, thus leaving the latter behind as anundistillable residue. Further details concerning the source, nature andmethod of separation of extractive materials from the Wood of variousconiferous species of trees are to be found in articles by Arthur B.Anderson in Industrial and Engineering Chemistry, vol. 38, page 450(1946), and vol. 39, page 1664 (1947) The wood extractive materialscharacterized by the source and composition described above have,

when incorporated in consolidated composition products, a mostsignificant and desirable influence on the strength and water resistanceof the latter. For example, as will appear more fully in the examplesbelow, when a hardboard is made from Ponderosa pine wood having itsnormal extractive content of 34% by weight, the water absorption of theboard is 51% by weight, and the modulus of rupture is 4580' pounds persquare inch. However, a hardboard prepared from Ponderosa pine massedpitch wood containing 34% by Weight extractives and prepared undersimilar conditions has a Water absorption of only 4% by weight and arupture modulus of 67 00 pounds per square inch. Hence, without the useof added hinder, or of added sizing material, but utilizing a materialheretofore discarded as waste or left unharvested in the forest areas,it is possible to prepare a product having a strength far above thestrength of the conventional commercial hardboards and a waterresistance well within the usual specifications therefor (i. c. withinthe 20% water absorption required by Federal hardboard specifications).

Furthermore, the inclusion of wood extractive materials as disclosedherein in the manufacture of consolidated composite products made fromwoody material overcomes completely one of the most troublesometechnical difiiculties accompanying their manufacture. This is theproblem caused by the sticking of the consolidated products to themembers of the hot presses in which they are formed and the fouling andclogging of the wire screens used in the presses to promote the removalof moisture from the product during pressing. In attempts to solve thesedifiiculties, which commonly result in the production of defectiveconsolidated products, numerous expedients have been employed. Thusspecial metals such as chromium, stainless steel, or iron coated withits magnetic oxide have been used to make the caul plates interposedbetween the material to be pressed and the platens of the press.Alternatively, the caul plates have been coated with lubricatingmaterials designed to prevent the sticking of the pressed substance.Commonly used lubricants at the present time are the silicone resinswhich, at current prices, cost from $7 to $10 per pound. Use of thesevarious expedient obviously adds substantially to the cost of thematerial, and even when they have been used, it has been necessary tointerrupt the press schedules from time to time in order that the pressplatens, caul plates, and particularly the screens may be cleaned andfreed from adhering sticky material.

Although it might be anticipated that the inclusion of substantialproportions of the wood extractive materials in the woody materials tobe consolidated would increase, rather than decrease the problem ofsticking, we have found exactly the contrary to be true. In spite of thesticky, pitchy nature of these materials at ordinary temperatures, whenthey are incorporated in a mass of woody material in substantial amountsand the resulting mixture is pressed at elevated temperatures, theextractive materials become fluid and act as very effective lubricatingagents, preventing sticking of the consolidated products to the caulplates and the fouling and clogging of the screen.

Surprisingly, also, these extractive materials do not tend to developundesirable properties when permitted to remain on the press as a seriesof boards or other products are made therein.

Whenever the press is cooled, the extractive materials solidify, forminga varnish-like coating over the caul plates. However, when the press isreheated, this coating again becomes fluid and, together with theextractiv materials contained in the freshly inserted blanks, serve aseffective lubricants to prevent the sticking of the latter. As a result,blank after blank may be consolidated in the press, each consolidatedproduct being freely removable from both the caul plate and the screen.

It is interesting and significant to note that, although th extractivematerials as originally incorporated in th mixtures to be hot pressedare sticky, gummy materials, the consolidated products resulting fromthe hot pressing operation have, at normal atmospheric temperatures, nosticky qualities whatsoever. On the contrary, they have smooth, glossydry surfaces maldng them admirably adapted for use in the ordinaryapplications. In view of the very substantial amount of extractivematerials used in the prod ucts, this indicates that, during the hotpressing operation, th extractive materials actually combine chemicallywith the lignin or other constituents of the woody materials. Thisconclusion is further buttressed by the very high strength values notedabove which characterize the product formed by the practice of thepresent invention, and which indicate a very pronounced binding effectexerted by the extractive materials.

In making the composite fibrous products of the present invention, woodymaterial from a suitable source and comprising, for example, woodparticles, wood fiber, or fiber derived from vegetable sources such ascorn stalks, sugar cane or straw is mixed with suitable proportions ofthe extractive material, and the resulting mixture formed into compositeproducts by either wet forming or dry forming procedures. Sufiicient ofthe extractive material is used to impart the desired degree of strengthand water resistance to the products. The lower limit of such usecomprises that value at which the striking effect on increasing thesevalues of the extractive materials becomes apparent. This is about 5% ofweight, based on the dry weight of the fibrous product. The upper limitof extractive use comprises that value at which, principally because ofthe pitchy, resinous character of the wood extractive material,difiiculties such as blooming, off color, blistering, etc. areencountered during the forming operation. This is about 45% of weightbased on the dry weight of the fibrous products. The preferred rangewithin which the desirable properties of strength and water resistanceare substantially fully developed in the case of extractive materialsfrom most coniferous wood species lies between about 8% and about 25% byweight, based on the dry weight of the final product.

Although in the formation of the hardboard or other composite fibrousproduct the wood extractives from any of the indicated sources may beadded per se, after isolation from the woody matrix in which it wasdeveloped, it is preferred to employ as a' raw material the knots, stumpwood, massed pitch and other wood fractions in which the extractivematerials are concentrated. These thus are employed as sources not onlyof the extractive materials, but also of substantial amounts of thecellulosic fiber which comprises the principal substance of the product.

Hence the herein described composite products may be made by reducing tofiber or particle form a sufficient amount of extractive rich materialsto provide from 5% to about 45% preferably from about 8% to about 25% byweight based upon thedry weight of the final product, of woodextractives and mixing therewith the desired amount of wood fiber orother lignocellulose' then may be formed into a felt and pressed betweenthe platens of a hot press at, for example, from about 200 to about1,000 pounds per square inch and from about C. to about 300 C. for atime of from about 10 minutes to about 30 minutes.

If a wet felting operation is contemplated, the

mixture of wood extractive material and cellu-.

losic fiber prepared as indicated above, but admixed with water to forma pulp, may be run onto a wire to form a wet lap in conventional manner.The latter after slight consolidation, may be dried in a dry room, ovenor similar equipment to produce a porous insulation board. On the otherhand, if it is desired to form a hardboard by wet forming techniques,the wet lap is consolidated between the platens of a hot press under thegeneral conditions of time, temperature and pressure indicated above,preferably at from about 200 p. s. i. to about 500 p. s. i. and fromabout C. to about 250 C. for from about 15 minutes to about 25 minutes.During the hot pressing of both dry felts and wet felts, it may bedesirable to breathe the press from time to time to permit the escape ofsteam and volatile materials contained in the wood extractives and thuspromote the formation of a product free from blisters and surfacedefects.

In the event that it is desired to insure thorough distribution of atleast the acidic constituents of the Wood extractive materialsthroughout the fibrous mass from which the composite products areformed, and thus insure the maximum degree of strength and Waterrepellency, the mixture of cellulosic material and wood extractives maybe subjected to a treatment with alkali,

preferably during the steaming operation. This converts the acidicmaterials, which normally are water insoluble, to their water solublesalts which are dispersed thoroughly throughout the pulp mixture. Then,upon treatment with an acid, these salts are converted again to the freeacids which are deposited uniformly on the cellulosic fibers.

Any basic material which is a sufiiciently strong base to dissolve theacid constituents of wood extractives may be employed for this purpose.Although the basic acting compounds of the alkali metals, for examplesodium hydroxide,

potassium hydroxide, sodium carbonate and potassium carbonate arepreferred, other bases such as ammonia, ammonium hydroxide, and thevarious strong, organic bases also may be employed.

Acids which may be used to regenerate the wood extractive acids anddeposit them upon the cellulosic fibers in the manner indicated abovecomprise in general any acids which are stronger than the woodextractive acids and therefore 7.. willreplace them from their salts.Such acids include generally the stronger mineral and organic acids,such as hydrochloric acid, sulfuric acid, phosphoric acid. acetic acid,and the like. Strongly acid salts such as alum also may be used.

The composite fibrous products of the invention and their waterresistance and strength qualities are illustrated in the followingexamples wherein the amounts of the constituents are expressed in partsor per cent by weight. In each example, the board products were made byreducing normal wood and the desired quantity of extractive rich wood tochip form. The chips then were defiberized, with or without priorsteaming, and formed into a pulp. Extraneous size (if used for purposesof comparison) was added to the plup, after which the latter was wetformed on a screen and the wet sheet hot pressed under the indicatedconditions of pressure, temperature and time.

The one-quarter-inch hardboards resulting from the foregoing proceduredid not stick to the press, and when removed, were non-stickythemselves, had a density of about 1 and were of a uniform, light browncolor. The strength and water repelling qualities of each sample weremeasured by standard test methods. The moisture absorption and thicknessswelling were determined by soaking weighed samples in water at 70 F.for 24 hours and determining the increase in weight and increase inthickness at the end of this period. The moisture absorption then wasexpressed as per cent by weight of the original weight of the sample,and the thickness swelling as per cent increase of the originalthickness. The strength characteristics were determined by subjectingthe samples to the conventional test method for measuring the flexuralstrength (modulus of rupture on flexing) this being expressed in poundsper square inch.

Example 1 One part Ponderosa pine stump wood (31% acetone solubleextractives) and three parts Douglas fir wood chips were steam treatedfor 30 minutes at 100 pounds steam pressure in a rotating digester. Thesteamed chips then were defiberized and formed into a pulp in a serratedmetal disc grinder. The resulting pulp mixture was wet formed and thewet sheet pressed at 500 p. s. i. for 20 minutes at 374 F. Theonequarter-inch hardboard formed in this manner had a water absorptionof 3.6% whereas a board formed as a control under identical conditionsfrom stump wood-free pulp had a water absorption of 49%.

Example 2 1 part Ponderosa pine knot chips (33% acetone soluble extract)and 3 parts Douglas fir.

Example 3 1 part Pondercsa pine knot chips (33% acetone solubleextract), 2 parts Douglas fir bark, and 5 parts Douglas fir wood chipswere steamed at 100 pounds pressure for 30 minutes, after which theywere defiberized and pulped. The resulting pulp mixture was wet formedand pressed into one-- Example 4 Ponderosa pine stump heart wood in chipform containing from 11% to 14% acetone soluble extractives was steamedat p. s. i. for 30 minutes. The steamed chips then were defiberized,formed into a wet mat, and pressed at 375 F. for 20 minutes using aplaten pressure-time cycle of 50040-500 p. s. i. and for 2-3-15 minutes.The resulting board had a water absorption of 10.1%, a thicknessswelling of 8.2%, and a rupture modulus of 6.170 p. s. i.

As a control, Ponderosa pine wood containing about 4% extractives wasformed into a board under the same conditions as set forth in the aboveparagraph. The board had a water absorption of 51.0%, a thicknessswelling of 24.5%, and a rupture modulus of only 4,580 p. s, 1.

Example 5 Using the procedure outlined in Example 4, a one-quarter-inchhardboard was made using 50% massed pitch Ponderosa pine wood containingfrom 26% to 34% extractives and 50% normal Douglas fir wood chipscontaining 3% to 4% extractives. The water absorption of the resultingboard was 5% and the modulus of rupture 6600- p. s. i.

Example 6 Again using the procedure of Example 4, another hardboardsample was made using 50% sugar pine knots containing 24 to 30%extractive materials and 50% normal Douglas fir wood chips. The modulusof rupture of the resulting board was 6,000 p. s. i.

Erample 7 Again using the procedure of Example 4, another hardboardsample was made using 50% Ponderosa pine knots containing about 25%extractives and 50% Douglas fir wood chips. The water absorption of theboard was 5% and the modulus of rupture 5,000 p. s. 1.

Example 8 Another board product was made from 100% massed pitchPonderosa pine wood containing 34% extractive materials. lhe procedureemployed was the same as that employed in Example 4 except that thepressure in the press was applied intermittently, a pressure of 500pounds per square inch and a temperature of 375 F. being employed forone minute, the press then breathed for two minutes, the same pressureand temperature applied for another minute, and the press then breathedfor two minutes, this sequence being continued until a total of twentyminutes had elapsed. The hardboard formed as a result of the foregoingoperations had a water absorption of 4% and a modulus of rupture of 6700p. s. i.

A series of six boards was made using the foregoing procedure, withoutcoating the caul plates with a special lubricant, or cleaning the platesor the screen between each pressing operation. In no instance did theboards stick to the press or the screen become fouled or clogged.Furthermore, at the end of the series, both screen and caul plates wereclean and ready for application to the production of additional boards.

. Example 9 To illustrate the deleterious effect of conventionalsizing'materials on the'strength of condition of 3% rosin size.The-board in which size was omitted had a water absorption of 52% and arupture modulus of 4400 p. s. i. The addition of the size reduced thewater absorption of the product to 5.1%, but also reducedthe strength ofthe board to 3100 p. s. i.

E zrample 10 1 part Ponderosa pine stump wood (31% acetone solubleextractive) and 7 parts Douglas fir Wood chips together with 1% byweight soda ash were steamed at 100 pounds pressure for 30 minutes. Thepressure was reduced to atmospheric and alum added until the mixture hada pH of 4.2. The mixture then was agitated for 10 minutes to precipitateon the fibers the acidic materials deriving from the wood extractives,which had been converted to their water soluble sodium salts by theaction of the soda ash.

The resulting pulp mixture was processed into a one-quarter-inch boardusing the procedure of Example 2. The board product had a waterabsorption of 10.5%.

It is apparent from a consideration of the above examples that theinclusion in composite fibrous products of from to 45% by Weight,preferably from 8% to 25% by weight, of wood extractive materials ishighly effective in increasing the water resistance and hence thedimensional stability of the products. As indicated in Example 1, theuse of about 8% extractives derived from Ponderosa pine stump wooddecreases the Water absorption of hardboards made therefrom from 49% to3.6%. Contemporaneously with the great increase in water resistance,there is a very significant increase in board strength. As is apparentfrom Example 4, the incorporation of from 11 to 14% of extractivematerials increases the rupture modulus of the fibrous products in whichthey are contained from 4580 p. s. i. to 6170 p. s. i. to the productsalso is apparent from Examples 5, 6 and 8, the products describedtherein having rupture moduli of 6600, 6000 and 6700 p. s. 1.,respectively. These results are particularly impressive when it isrealized that the rupture moduli of comparable structural, untemperedhardboards currently on the market lie within the range of 2500 to 4000p. s. i. They lend strength to the theory that the wood extractivematerials in addition to serving as water resistant agents, also serveas highly effective binders in the fibrous products in which they arecontained.

The economic advantages stemming from our invention are immediatelyapparent. By utilizing our process, it is possible to form hardboard andother fibrous products of superior strength and water resistance whileeliminating the use of extraneous binders and sizing agents. Hence thecost of these materials, and the very sub stantial cost of the labor,time and equipment necessary for their inclusion, is eliminated. Inaddition one of the most troublesome problems encountered in formingconsolidated products from Woody materials, i. e. sticking of theproduct to the press and clogging of the screens used The high strengthimparted therein is overcome substantially completely. Furthermore, andof particular interest, is the fact that these desirable results areaccomplished through the use of stump wood, knotty wood, massed pitchwoods and similar materials which heretofore have been classed aslogging and sawmill waste, and either not harvested, or discarded in themill.

It will be apparent that our water resistant products aredistinguishable from products containing conventional rosin size. In thefirst place, as has been brought out in detail, the wood extractivematerials which are the subject matter of our invention are complexmixtures of substances including fatty acids, phenolic compounds,terpenes, esters, sterols, fats, waxes, resins and the like. Rosin size,on the other hand, consists almost solely of rosin acids. Furthermore,although rosin serves to increase the water resistance of fibrousproducts in which it is contained, it does not serve as a binder and, infact, materially reduces the strength of boards and products in which itis contained (Example 9). The wood extractives, on the contrary, serve adefinite binding function and impart a very high degree of strength tothe products in which they are used.

Having thus described our invention in preferred embodiments, we claim:

1. A fibrous composition board essentially comprising difibratedlignocellulose consolidated with such proportion of defibratedconiferous lignocellulose rich in acetone-soluble content that the wholeacetone-soluble content of the total lignocellulose material amounts to5 to 45 per cent of the dry weight of the board.

2. A fibrous composition board essentially comprising defibratedlignocellulose of coniferous trees consolidated with such addedproportion of defibrated coniferous lignocellulose rich inacetone-soluble content that the whole acetonesoluble content of thetotal lignocellulose material amounts to 8 to 25 per cent of the dryWeight of the board.

3. A fibrous composition board essentially comprising defibratedlignocellulose of coniferous trees consolidated with such proportion ofDouglas fir lignocellulose rich in acetone-soluble content that thewhole acetone-soluble content of the total lignocellulose materialamounts to 5 to 45 per cent of the dry weight of the board.

4. A fibrous composition board essentially comprising defibratedlignocelulose of coniferous trees consolidated with such addedproportion of Ponderosa pine lignocellulose rich in acetonesolublecontent that the whole acetone-soluble content of the totallignocellulose material amounts to 5 to 45 per cent of the dry weight ofthe board.

5. A fibrous composition board essentially comprising defibratedlignocellulose of coniferous trees consolidated with such addedproportion of defibrated Southern pine lignocellulose rich inacetone-soluble content that the whole acetonesoluble content of thetotal lignocellulose material amounts to 5 to 45 per cent of the dryweight of the board.

6. A fibrous composition board essentially comprising defibratedlignocellulose of coniferous trees consolidated with an added portion ofdefibrated coniferous lignocellulose rich in acetonesoluble content,said portion of lignocellulose being selected from the group consistingof the stump wood, knots and massed pitch of coniferous trees and beingin such proportion that the while acetone-soluble content of the totalligno- Number Name. Date cellulose material amounts to 5 to 45 per cent1,652,218 Talllmain Dec. 13, 1927 of the dry weight of the board.2,090,758 Hoflin V L .L Aug, 24, 1937 7. A fibrous composition boardessentially 2,264,189 Richter Nov. 25,1941 comprising defibratedlignocellulose of coniferous 5 2,276,304 Hunter ,A L..- Mar. 1'7, 1942trees consolidated with an added portion of de- 2,427,966 Hirschler ..vSept. 23, 1947 fibrated coniferous lignocellulose rich in acetonesolublecontent, said portion of lignocellulose FOREIGN PATENTS being selectedfrom the group consisting of the Number Country Date stump wood, knotsand massed pitch of conifer- 10 441,152 France July 1912 ous trees andbeing in such proportion that the 38936 Germany 2, 1387 wholeacetone-soluble content of the total ligno- OTHER REFERENCES 1 i l ig ig g gg g? 8 to 25 per amt of the dry slgegvli sz Mechanical Engineering,65 (1943),

15 Vinsol Resin, Hercules Powder 00., Wilming- References Cited in thefile of this patent ton, Delaware, March 1939, pages 21 and 22.

UNITED STATES PATENTS Number Name Date 251,023 Boyd Dec. 20, 1881

1. A FIBROUS COMPOSITION BOARD ESSENTIALLY COMPRISING DIFIBRATEDLIGNOCELLULOSE CONSOLIDATED WITH SUCH PROPORTION OF DEFIBRATEDCONIFEROUS LIGNOCELLULOSE RICH IN ACETONE-SOLUBLE CONTENT THAT THE WHOLEACETONE-SOLUBLE CONTENT OF THE TOTAL LIGNOCELLULOSE MATERIAL AMOUNTS TO5 TO 45 PER CENT OF THE DRY WEIGHT OF THE BOARD.